The present invention relates to a floor covering of electric conducting type for use in premises where it is desired to avoid static electricity by grounding. Such coverings have been developed in several types, e.g. so-called carbon mats, but a common feature for all coverings is that focus is on the grounding ability to such an extent that other qualities in a floor covering have not been particularly considered. It is presumed that the crucial point is the grounding ability in such a special floor covering as the appearance of major static charges, let alone even very small sparks, can have dire consequences and it is considered of secondary importance whether the floor covering is reasonably appropriate in all other respects, e.g. with regard to walking and standing comfort, cleanability, wear resistance etc., even to a certain degree price.
The present invention breaks with this concept and its purpose is to provide a floor covering which, while fully allowing for grounding ability, at the same time widely provides for all other requirements for floor covering in working premises.
The invention is based on the recognition that exceedingly appropriate floor coverings have already been developed which, true enough, have not been provided with grounding qualities, but which may be easily modified to also show this capacity without such modification in any way harming the other good qualities as adapted to the purpose.
Reference is here made to floor coverings of plastic tiles of the type having principal dimensions of the magnitude 25.times.25.times.2 cm and being designed with an unbroken or perforated top plate which is supported at a number of integral rib or stud parts protruding downwards therefrom, with the rib or stud parts being mutually spaced and supporting the top plate on an underlying firm floor surface. Additionally the tiles are designed so that they can be laid closely against one another in a mutually interlocking fashion. It has been ascertained that floor coverings of this type have a multitude of advantages for a variety of reasons, regarding as well usability as maintenance and mounting. By the invention it is recognized that none of these good qualities will be sacrificed by the simple measure of manufacturing the tiles of a plastic material of the special kind having good electrical grounding abilities. Contradictory to the above view it could be said that such an intended ideal floor covering so far has been developed without consideration for the special quality that for certain uses it is desirable that the covering is electrically groundable.
It is not immediately particularly conspicuous that a covering built of relatively small, die-cast tile members can qualify as a groundable flooring, which in principle ought to be spread over a large area, but it is realized by the invention that often only relatively restricted areas having grounding qualitites are required, e.g. at permanent seats or standing room at existing worktables, and even though the tile elements in an electrically conducting version will be more expensive to produce than corresponding non-conducting elements, the corresponding increase in cost can, however, be limited to the partial areas concerned, while the flooring as a whole can appear in a uniform way. Especially as die-cast, comparatively small covering elements are used, the employment of the more expensive, electrically conducting elements can easily be limited to precisely the actual walking or standing areas.
In the light of this the covering according to the invention is characteristic in that it includes modular elements of intercoupled plastic tiles of the type being designed with an optionally perforated resilient stepping plate which at its bottom side has a number of mutually separated downward projecting supports and along the edges is provided with coupling means enabling the tile to be interlocked with an adjacent tile, with the entire floor covering is divided into two or more partial areas, that is one or more relevant subareas with tiles having electrical conducting ability and one or more subareas with tiles having no such ability.
The type of tile elements considered here has the advantage that the resulting flooring can be adapted extensively to various or changed positions of machinery beds and other primary limitations to the floor space in that the tile elements conveniently can be taken up and relaid anywhere, as they are stabilized only by their interlocking with other corresponding tile elements. Correspondingly any subarea consisting of conducting tiles may be established anywhere.
As another major advantage the tile elements of the considered type are "foot kind" in the sense that their top plates are resiliently flexible in the areas between the bracing supports, whereby a quite substantial therapeutical effect on the user's feet is achieved. This major advantage can be fully maintained by the invention because the effect in question is not much influenced by the material being of electrically conducting or non-conducting plastic.
The plastic tiles have the further advantage that they are easily cleaned, and this advantage is not jeopardized by using plastic of the electrically conductive type in the manufacture. The covering can simply appear exactly as before.
For the intended effect it obviously does not suffice that the tile elements themselves be electrically conductive, as they should also be effectively grounded. When placed on a support floor which in itself has a sufficient grounding ability, the grounding can be effected immediately through the tiles where the relevant current path down through the support parts will be comparatively short, i.e. the tiles may or must have only a low conductivity, whereby they can be correspondingly inexpensive. No improvement of the grounding will be obtained through the use of the tiles, but it is achieved that the walking or standing persons get a considerably improved floor surface to walk or stand on, that is the same improved floor surface which is also found at the less critical grounding subareas where it is advantageous and acceptable to place the less expensive, non-conductive tiles.
When building up the flooring on a non-ground floor the problem is entirely different, as a grounding with comparatively long current paths in the horizontal direction to a suitable ground connection is required. Underneath the tiles a grounded metal foil can be placed, but this solution is none too attractive. As the tile elements are joined by special interlocking means they could also hereby be electrically interconnected, but it is considered dubious to rely on the necessary perfect contact always being established hereby. Admittedly the engagement parts could be optimized from an electrical contact point of view, but the fact remains that for an efficient grounding from a single point of a large floor area an almost metallic conductivity in the material would be required, and it is a fact that the plastic material for the actual purpose is substantially more expensive, the higher the conductivity is to be.
According to the invention the low-cost of the material as well as a high grounding safety of even a large floor space are considered by producing as a standard the individual tile elements with an embedded, central contact member which at the laying of the tile is suited to be directly wire connected with the contact members of the other elements, whereby it suffices to ground the net of highly conducting wire connections in question at a single spot or at several places where large areas are concerned. Hereby, irrespective of the area of the floor space, the individual tile elements only have to be made in such a way that with a required efficiency they can conduct electricity away from their own small area, even limited to the area parts between the edge and the center of the element, which in practice means a maximum distance of some 20-30 cm. Normally, this will be possible by means of an only moderately conducting plastic material, i.e. a reasonably inexpensive material.
When using the wire connections mentioned, it is pertinent to lay out wires on the rigid floor space underneath the tile elements which, however, can be done without any special problems provided some lower recesses are provided in the edge ribs supporting the elements at the floor. It should be mentioned that the known tile elements are already provided with such recesses, as they are already prepared for use on floor spaces where either laid out wires occur, e.g. exhibition stand floors, or where water should be able to be drained off.
It should be noted that the plastics in question must necessarily be produced by die-casting from a basic material which in itself is pronouncedly electrically insulating, i.e. a conducting material must be incorporated which can create the required moderate conducting ability. In practice a conducting fibre material ought to be used, preferably carbon fibres, and practice has shown that when die-casting such a composite material, it is rather dubious whether the resulting tile will attain the required conducting ability in the horizontal and/or vertical direction between different surface parts thereof, because the fibres do not necessarily remain in a homogeneous admixture within the material by the injection thereof into the compact mould. Therefore it has been found necessary to subject every single tile member produced to a control measuring of the conductivity in the horizontal and vertical direction, respectively, and it has been found hereby that a considerable percentage of rejects may occur, which of course will contribute to the conducting tiles generally being appreciably more expensive than the pure plastic tiles.